1. Field of Invention
The invention relates to a brake apparatus for a moving apparatus driven by a linear motor that is applied to a machine tool or a factory facility.
2. Description of Related Art
A linear motor is applied to an apparatus when a stator mounted to a member on a stationary side, and a movable member mounted to a member on a movable side, are disposed so as to face each other across an air gap. As such, a linear driving force of the linear motor moves in a movable direction when the apparatus is in an energized state. In a conventional moving apparatus driven by the linear motor, a sudden slowdown and a sudden stop can be performed by an electrical control. However, when the power supply to the linear motor is interrupted because of a power failure or a break in a cable, or when the linear motor is stopped in an emergency, electrical control is rendered inoperable. As a result, the member on the movable side (hereinafter referred to as the movable member side) moves into an inert running state. To avoid this problem, a mechanical brake device is provided, with the electrical control device.
One particular mechanical brake device uses a brake that drives at a cylinder, with a member on the movable member side, and a brake pad of the brake pressed against a friction member provided with a member on the stationary side (hereinafter referred to as the stator side), to cause the member on the movable member side to brake. In this case, it is possible to obtain a high brake force at the cylinder, however, the braking response is slow because the time required to move fluid is long compared with the electric signal. Another particular mechanical brake devices uses a magnetic brake, which utilizes an electromagnet and an elastic body such as a spring, with the member on the movable member side. When the power supply to the linear motor is interrupted or the linear motor is stopped in an emergency, a brake pad of the magnetic brake is pressed against a friction member on the stator side through the use of an elasticity of the elastic body, to cause the member on the movable member side to brake. However, during braking, the brake pad of the magnetic brake has to maintain a large surface to receive the pressure therefrom. Accordingly, this increases the size of the moving apparatus.
Japanese Laid-Open Patent Publication No 10-112971 discloses a moving apparatus in which a ferromagnetic plate, having a brake pad, is disposed with a travelling slider, which is a member on the movable member side, via an electromagnet and an elastic body, such as a spring, and a friction member disposed with a member on the stator side. In the moving apparatus, when a power supply to the linear motor is interrupted or the linear motor is stopped in an emergency, the ferromagnetic plate adhered to the electromagnet is separated there from and the brake pad is pressed against the friction member by attraction between the ferromagnetic plate and a fixed magnet as the stator in order to brake the travelling slider. As the attraction works between the ferromagnetic plate and the fixed magnet, an external actuator device, so as to separate the brake pad from the friction member at the start of a normal operation of the linear motor, is also disposed to the travelling slider.
However, since the electromagnet, the elastic body, the brake pad, the ferromagnetic plate, and the external actuator device are disposed to the travelling slider on the movable member side, the number of parts for the mechanical brake device increases. As a result, the cost for the parts also increases. In addition, the increased number of parts brings about an increase in the weight on the travelling slider, a heavier electrical load on the linear motor, and increased costs. Furthermore, the increase in the number of parts increases the size of the travel ling slider, and by extension, the entire moving apparatus.
The invention provides a brake apparatus having sufficient braking in a simple structure for a moving apparatus driven by a linear motor.
In various exemplary embodiments of a brake apparatus for a moving apparatus driven by a linear motor, the linear motor having a movable member and a stator disposed so as to face each other across an air gap from each other, the moving apparatus having a first member attached to the movable member and a second member attached to the stator, the first member being moved along the stator when the linear motor is energized, the first member being allowed to move downward by gravity along the second member when the linear motor is not energized and the first member is within a moving range thereof, a movement of the first member being controlled electrically in a normal operation of the linear motor, the brake device comprises a cylinder device having a cylindrical member attached to the second member and a piston connected to the first member, the cylindrical member having both end portions including a cylinder end on a side of the first member and another cylinder end on the opposite side of the cylinder end, the cylindrical member defining a first fluid chamber between the piston and the cylinder end; a fluid supply source that supplies fluid under pressure to the first fluid chamber of the cylinder; a first regulating valve disposed on a fluid path between the first fluid chamber of the cylinder and the fluid supply source, the first regulating valve capable of opening and closing, the fluid flowing in the fluid path and the first fluid chamber while the first regulating valve is open and the fluid stemming in the fluid path and the first fluid chamber while the first regulating valve is closed; and a controller that opens the first regulating valve during normal operation of the linear motor and closes the first regulating valve either when power supply to the linear motor is interrupted or an emergency stop is instructed to the linear motor.
During a normal operation of the linear motor, the first regulating valve is opened by the signal from the controller, the fluid pressure is supplied to the cylinder device, and the brake apparatus functions as a counterbalance which can stably operate the first member supported at the piston independently of fluctuations in the load. When the power supply to the linear motor is interrupted or the linear motor is stopped in an emergency, the first regulating valve device is closed when a signal is not received from the controller, the fluid pressure is maintained in the cylinder device as it is just before the power supply is interrupted or the linear motor is stopped in an emergency, and the piston of the cylinder device is brought to a standstill. As a result, the first member, which is supported at the piston, can be completely stopped.
The braking is actuated through the use of a cylinder device that functions as a counterbalance of the moving apparatus during normal operation. Therefore, the invention eliminates the need for various parts for a mechanical brake device. As a result, cost reduction and weight reduction of the member on the movable member side can be achieved. The weight reduction of the member on the first member side lowers the capacity of the linear motor to the moving apparatus, which can contribute to the cost reduction. In addition, the entire moving apparatus can be downsized.
In another exemplary embodiment of a brake apparatus for a moving apparatus driven by a linear motor, the linear motor having a movable member and a stator which are disposed so as to face each other across an lair gap, the moving apparatus having a first member attached to the movable member land a second member attached to the stator, the first member moved along the stator when the linear motor is energized, a movement of the first member being controlled electrically in a normal operation of the linear motor, the brake apparatus comprises a double-acting cylinder device having a cylindrical member attached to the second member and a piston which is connected to the first member, the cylindrical member having both end portions including a cylinder end on a side of the first member and another cylinder end on the opposite side of the cylinder end, the cylindrical member defining a first fluid chamber between the piston and the cylinder end and a second fluid chamber between the piston and the another cylinder end; a fluid path member containing fluid, the fluid path member connected to the first and second fluid chambers at both end portions of the cylindrical member to provide fluid communication between the first and second fluid chambers; a regulating valve disposed on the fluid path member, the regulating valve capable of opening and closing, the fluid flowing in the fluid path member and the first and second fluid chambers while the regulating valve is open and the fluid stemming in the fluid path member and the first and second fluid chambers while the regulating valve is closed; and a controller that opens the regulating valve during normal operation of the linear motor and closes the valve either when power supply to the linear motor is interrupted or an emergency stop is instructed to the linear motor.
In this exemplary embodiment, during normal operation of the linear motor, the regulating valve is opened by the signal from the controlling device, and the fluid is moved freely in the fluid path. When the first-member operates, the fluid functions as a resistance against the double-acting cylinder, and the double-acting cylinder functions as a damper of the first member. When the power supply to the linear motor is interrupted or the linear motor is stopped in an emergency, the regulating valve device is closed when a signal is not received from the controller, the fluid pressure is maintained in the cylinder device, and the piston of the cylinder device is brought to a standstill. As a result, the first member, which is supported at the piston, can be completely stopped.
Therefore, the invention eliminates the need for various parts for a mechanical brake device. As a result, parts cost reduction and weight reduction of the first member can be achieved. The weight reduction of the first member lowers the capacity of the linear motor to the moving apparatus, which can contribute to the cost reduction. In addition, the entire moving apparatus can be downsized.
In another exemplary embodiment of the invention, the brake apparatus may farther include an oscillation absorber disposed on the first member, the oscillation absorber pressing against the second member either when power supply to the linear motor is interrupted or an emergency stop is instructed to the linear motor.
When a signal is cut off from the controller, the oscillation absorber is pressed against the second member to slow down the first member. Therefore, the oscillation absorber can increase the safety and the reliability so as to completely stop the first member.